Umbrella Fix

Umbrella's problem all these years was that FindListElem called on a nil
value returns nil, not 0. I fixed that, and standardized its distance
measurement function. It now functions completely as intended.

It adds 500 defense and up to 100% resistance to all magic to those within the umbrella. If this is something somebody else wants to balance or fix, we can do that later, but this is just a bug fix pull.